Vehicles such as aeroplanes require fuel tanks to store fuel for use in the vehicle's propulsion system. A known problem that can occur in an aircraft's fuel tank is that water builds up in the tank. For example, water vapour may enter a vent of a fuel tank and as the altitude of the aircraft increases and the temperature decreases the water vapour condenses within the tank and, due to water being denser than aviation fuel, settles at the bottom of the tank.
A known way of removing water from a fuel tank is to provide one or more valves to enable water to be drained from the tank upon activation of a valve. Different types of valve are used for this purpose. A direct drain valve drains water from an area adjacent the valve. An indirect drain valve includes a tube or duct, one end of which is connected to the valve conduit and the other is positioned at a remote location, such that water from the remote location can be drawn through the indirect drain valve. These two types of valve are structurally different to one another.
It is desirable to place a water drain valve at the lowest area or areas of the fuel tank. Where it is possible to do so, a direct water drain valve will generally be provided. However, where it is not possible to do so, for example because there is insufficient room to place a valve or from a structural perspective it is not desirable to cut a hole in the tank for a valve at that position, as may be the case with aircraft wings, an indirect water drain valve will be provided in the near vicinity and a tube will connect the indirect water drain valve to the drainage area. Thus, it will be appreciated that in some cases it is necessary to use two different types of valve within a single aircraft, or even within a single fuel tank.
Furthermore, it will be appreciated that a fuel tank can be made from a number of different materials. In order to provide a valve in the body of a fuel tank, the outer surface of the fuel tank generally has a recess formed in it. The recess corresponds in shape to a flange around the base of a valve. In some cases, to prevent rotation of the valve relative to the body, a hole will be drilled in a face of the recess for receiving a corresponding projection on the valve. For some materials, such as metal, it is relatively simple to form the hole within the recessed part for receiving the projection. However, when a fuel tank is made of a material such as carbon composite it can be difficult to machine the hole due to the size thereof.